1. Field of the Invention
The present invention relates generally to combinations of toner colorants that may be used for monitoring toner layer thickness in electrophotographic systems. More specifically, toner may be formulated to include infrared transmissive and/or infrared reflecting colorants that may be utilized to optimize the performance of a toner patch sensor. In particular, the infrared transmissive and/or infrared reflecting colorants may be specifically employed to provide black toners with improved toner patch sensitivity which black toner may optionally incorporate carbon black.
2. Description of the Related Art
Electrostatically printed color images may be produced by depositing toners of various colors onto a recording media, such as a sheet of paper. A wide palette of printed colors may be generated by printing yellow, cyan, magenta and black toners in various proportions and combinations. Each individual color of the producible palette may require a specific proportion and combination of toners. If the particular proportions of toner for a selected color cannot be repeatedly deposited on the printed media then the printed color may not be consistent and vary in hue, chroma, and/or lightness from attempt to attempt of printing. The proportion of each toner color to be deposited is controlled by the thickness of the toner layer of a given color and the halftone area coverage. Therefore, controlling the printed colors, and ensuring reproducibility of the printed colors, may be achieved by controlling the toner layer thickness to ensure consistent color reproduction.
Toner patch sensors have therefore been used in printers and copiers to monitor the toner density of unfused images and provide a method of controlling the print darkness. In color printers and copiers, the toner patch sensors may be used to maintain the color balance and in some cases to modify the gamma correction or halftone linearization as the electrophotographic process changes with the environment and aging effects. However, monitoring the amount of black toner on black intermediate belts or black paper transport belts is problematic due to the low optical contrast between the black toner and the underlying surface.